Field of the Invention
The present invention relates to an image pickup apparatus, such as a single-lens reflex camera, and more particularly to a technique for controlling the operation and driving of a quick return mirror, such as correction control of an output value from a photometric unit in driving the quick return mirror, and a technique for controlling the operation of the quick return mirror in strobe photographing.
Description of the Related Art
An image pickup apparatus, such as a single-lens reflex camera, is provided with a quick return mirror mechanism including a main mirror holder for holding a main mirror formed by a half mirror, and a sub mirror holder that holds a sub mirror and is rotatably supported with respect to the main mirror holder. The quick return mirror mechanism enters a photographing optical path (mirror down) to guide an object light flux having passed through a photographing optical system to a viewfinder optical system during viewfinder observation, and retracts from the photographing optical path (mirror up) to guide an object light flux to an image pickup device during photographing. Further, during viewfinder observation, the quick return mirror mechanism reflects an object light flux having passed through the main mirror by the sub mirror to guide the reflected object light flux to a focus detection unit (Japanese Patent Laid-Open Publication No. H09-274249).
For an image pickup apparatus of this type, there has been conventionally proposed a technique that changes an exit angle of light guided to a focus detection optical system to thereby make it possible to perform focus detection in a desired wide range in a vertical direction and a horizontal direction within a photographing range (Japanese Patent Laid-Open Publication No. 2001-83402).
The object light flux guided to the viewfinder optical system is divided into two light fluxes by a pentaprism, one of which is guided to an eyepiece lens, and the other of which is guided to a photometry sensor for photometry measurement. When the mirror unit is in the mirror-up position, an object light flux having passed through the photographing optical system is guided to an imaging surface of the image pickup device, and is photoelectrically converted.
Further, for strobe photographing, there has been proposed a technique in which preliminary light emission is performed when the main mirror is in a predetermined position, and a light emission amount for final light emission is determined based on a result of photometry by the photometry sensor during the preliminary light emission, so as to perform the final light emission for photographing (Japanese Patent Laid-Open Publication No. 2007-322895).
However, the mechanism disclosed in Japanese Patent Laid-Open Publication No. H09-274249 has the configuration in which the sub mirror holder is pulled up by the main mirror holder in the mirror-up operation, and hence the inertia force of the sub mirror holder acts when the main mirror holder performs the mirror-up operation. For this reason, there is a limit to the speed of the mirror-up operation, and the limit prevents reduction of the release time lag.
On the other hand, the technique disclosed in Japanese Patent Laid-Open Publication No. 2001-83402 has a problem that when a sufficient amount of light is to be guided to the focus detection optical system, the amount of light guided to the viewfinder optical system is reduced, which brings about a problem of a dark finder image. Further, in a case where part of a light flux guided to the viewfinder optical system is used for photometry by the photometry sensor, the accuracy of photometry is lowered particularly under a low luminance environment.
Further, the main mirror of the mirror unit is generally formed by a half mirror because it is necessary to guide a light flux to the focus detection unit. For this reason, the light amount of the light flux reflected to the viewfinder optical system is reduced by an amount of the light flux which reaches the main mirror and passes therethrough to the sub mirror side when the mirror unit is in the mirror-down position, whereby the amount of light guided to the photometry sensor is also reduced. Therefore, in the technique disclosed in Japanese Patent Laid-Open Publication No. 2007-322895, to obtain an accurate amount of final strobe light emission for a photographic scene which is dark with a large camera-to-object distance, or the like, it is necessary to increase the light amount of preliminary strobe light emission, which increases power consumption.